1. Field of the Invention
The present invention relates to an apparatus for conducting color image processing after color image information is converted into electric signals.
2. Description of the Prior Art
There is already known such color image processing apparatus in which a color original is read by scanning with an image sensor such as a charge-coupled device (CCD) through three color filters to obtain electric color information which is used for producing a color image through an ink jet printer equipped with ink emitting nozzles respectively emitting ink of three different colors.
FIG. 1 shows a conventional color image processing apparatus in a block diagram, wherein shown are an original 1; a light source 2; a lens 3; dichroic mirrors 4; CCD line sensors 5a, 5b, 5c; analog-to-digital (A/D) converters 6a, 6b, 6c; buffer memories 7a, 7b, 7c; a masking circuit 8; dither circuits 9a, 9b, 9c; ink jet printers 10a, 10b, 10c; a sheet feeding roller 11; tension rollers 12; driving rollers 13; a copy 14; and a supporting plate 15. In the following drawings, components the same as those shown in FIG. 1 will be represented by the same numbers. The suffixes a, b and c indicate components related with three primary colors after color separation.
In FIG. 1, the original 1 is illuminated by the light source 2 to color separate the image information of said original 1 into the color components of blue, green and red through the lens 3 and the dichroic mirrors 4. Thus separated color components are photoelectrically converted into electric signals by means of the CCD line sensors 5a, 5b, 5c. The analog image signals of blue (B), green (G) and red (R) colors are converted, in the A/D converters 6a, 6b, 6c, into digital signals, which are subjected to modification of the transfer speed in the buffer memories 7a, 7b, 7c. Then, the signals B, G, R suitable for additive mixing are converted into signals of yellow (Y), magenta (M) and cyan (C) suitable for subtractive mixing in the masking circuit 8, which also processes each signal in relation to other signals for achieving correction in consideration of the spectral characteristics of the yellow, magenta and cyan inks. Said signals Y, M, C are binary digitized through comparison with a predetermined threshold matrix in the dither circuits 9a, 9b, 9c to activate ink jet printers 10a, 10b, 10c equipped with ink emitting nozzles corresponding to the signals Y, M, C, thereby simultaneously printing three colors on a printing sheet supplied from the feeding roller 11, thus obtaining the color copy 14 of the original 1.
In the present example, the dimensional errors in the image magnification among the signals B, G, R are practically negligible since the color signals B, G, R are produced through a common lens 3 and CCD line sensors 5a, 5b, 5c which are manufactured dimensionally uniform by a photoetching process. Dimensional errors include errors in the dimensions of the color-separated images in the reproduction of the original image, by means of the ink jet printers in the present example, giving rise to positional color aberrations in the synthesized image. It is however extremely difficult to deposit the inks from the ink jet printers 10a, 10b, 10c onto the same position.
In order to avoid the above-mentioned difficulty, there is proposed, as shown in FIG. 2, an apparatus for positioning the ink jet printers 10a, 10b, 10c at determined intervals. In such arrangement, in order to cover the differences in the writing time of different colors by the ink jet printers 10a, 10b, 10c, it becomes necessary to use an unrepresented page memory.
Also the use of three independent optical systems gives rise to non-negligible dimensional errors in the image magnification among different color images due to an influence of mechanical imprecision. For this reason it is considered to regulate the image magnification of each color with zoom lenses 17a, 17b, 17c as shown in FIG. 2 projecting the image through respective optical elements 16a, 16b, and 16c to the respective CCD line sensors 5a, 5b, and 5c.
Such arrangement is however undesirable because it involves precise and inevitably expensive zoom lenses and in addition requires cumbersome optical adjustment.
Furthermore, in case of arbitrarily modifying the magnification of a color image on a document, there has conventionally been required a complicated structure for each separated color.